body{
    margin: 0;
    padding: 0;
}

a{
    /*消除下划线*/
    text-decoration: none;
}

.nav a {
    /*color: #fdfffe;*/
    color: black;
    padding: 0 10px 10px 10px;

}
.nav {
    list-style: none;
    height: 30px;
    /*border-bottom: 10px solid black;*/
    /*border-top:8px solid black;*/
    margin-top: 22px;
    padding-left: 50px;
    font-weight: bold;
}

.nav li {
    float:left
}
.nav li a {
    display:block;
    height:30px;
    text-align:center;
    line-height:30px;
    /*background:black;*/
    background:#fdfffe;
    margin-left:10px;
}
/*.nav li a.on, */
.nav li a:hover {
    color: #67b803;
    padding: 0 10px 10px 10px;
    border-bottom: 3px solid #67b803;
}

.top_bar{
    width: 975px;
    height: 70px;
    margin: auto;
    /*border-bottom: 1px dashed black;*/
}

.top_bar span{
    margin-top: 10px;
    float: left;
    display: block;
}

.top_bar ul{
    float: right;
    display: block;
}

.null{
    margin: auto;
    width: 1905px;
    border-bottom: 2px dashed black;
}